This invention relates to an improved process for producing a mixture containing cyclohexanol and cyclohexanone. More particularly, the invention relates to an improvement in the catalytic process for production of a mixture containing cyclohexanol and cyclohexyl hydroperoxide wherein cyclohexane is oxidized in air to produce a reaction mixture containing cyclohexyl hydroperoxide (CHHP) and the cyclohexyl hydroperoxide is decomposed.
The principle products of the decomposition, cyclohexanone and cyclohexanol, are readily converted by oxidation to adipic acid. Adipic acid is used in large volume in the preparation of condensation polymers, particularly polyamides.
The oxidation of cyclohexane to mixtures containing cyclohexanones and cyclohexanol is a well-known, competitive, large-volume industrial process. The product is frequently referred to as K/A (Ketone-Alcohol) mixture. Experience in the operation of the process which is reflected in the disclosures of many patents, has taught that the oxidation must be carried out at low conversion, if it is desired to maximize the yield of K and A and to minimize the formation of other oxidation products, some of which have deleterious effects in the production of adipic acid and/or on the purity of the adipic acid produced. Relatively minor process improvements, such as in the yield of K and A, can result in highly beneficial cost advantage.
Patents directed to the oxidation of cyclohexane include U.S. Pat. Nos. 2,675,407; 3,093,686; 3,530,185; 3,917,708; 3,957,876; 3,987,100; and 4,341,907.
An important step in the rather complicated overall oxidation process is the decomposition of cyclohexyl hydroperoxide, which is a primary oxidation product of cyclohexane. Since the efficiency of this decomposition step contributes to the efficiency of the overall oxidation process, improvements in the decomposition of CHHP are a desirable objective.
A number of ways of decomposing CHHP have been described.
U.S. Pat. No. 2,609,395, issued to Dougherty et al. on Sept. 2, 1952, discloses a process for oxidation of cycloalkanes to produce cycloalkanols and cycloalkanones, wherein a cycloalkane is reacted with limited quantities of oxygen. The cycloalkane hydroperoxides thereby produced are decomposed by heating in the presence of a cycloalkane, producing cycloalkanols and cycloalkanones.
U.S. Pat. No. 2,851,496, issued on Sept. 9, 1958 to Cates, Jr., et al., discloses a process for oxidation of naphthenes, particularly cyclohexane, in the liquid phase using a gas containing molecular oxygen followed by destruction of the resulting hydroperoxide by including in the overall process, after from 1 to 12% or more of the naphthene molecules have been oxidized, a controlled decomposition of peroxides on a bed of solid catalyst in the absence of any reducing agent or oxygen. Suitable catalysts include solid metallic substances in the form of granules, preferably comprising an inert supported impregnated with a metal of group VIII or an oxide of a metal of group VIA.
U.S. Pat. No. 3,923,895, issued to Costantini et al. on Dec. 2, 1975, discloses a process for the preparation of a mixture of a cycloalkanone and cycloalkanol by oxidation of a cycloalkane in the liquid phase by means of a gas containing molecular oxygen, following by heating the resulting solution of cycloalkyl hydroperoxide in the corresponding cycloalkane, at 80.degree.-150.degree. C., in the presence of a soluble chromium derivative as a catalyst, wherein at least a part of the heating of the hydroperoxide solution is carried out in the presence of a monoester or diester of orthophosphoric acid which is soluble in the reaction medium. Suitable compounds include alkyl, cycloalkyl, aryl and aralkyl esters. The process is said to minimize the formation of insoluble product which reduces heat exchange across the walls of the apparatus being used by coating thereon.
U.S. Pat. No. 3,925,316, issued to Brunie et al. on Dec. 9, 1975, discloses a process for preparing a mixture of cycloalkanol and cycloalkanone, particularly cyclohexanol and cyclohexanone, consisting of heating a solution of a cycloalkyl hydroperoxide in the corresponding cycloalkane in the presence of a catalyst which is a soluble derivative of vanadium, molybdenum or ruthenium. Suitable soluble catalysts include naphthenates, octoates, stearates and carbonyl derivatives. The process is stated to solve several previous problems including deactivation of the catalyst due to the formation of viscous polycondensates, such as polyesters.
U.S. Pat. No. 3,927,105, issued to Brunie et al. on Dec. 16, 1975, discloses a process for the preparation of a mixture of cycloalkanol and cycloalkanone, particularly cyclohexanol and cyclohexanone, which is rich in the cycloalkanone comprising heating a solution of a cycloalkyl hydroperoxide in the corresponding cycloalkane at from 80.degree. to 150.degree. C. in the presence of a soluble chromium compound as a catalyst, in a series of separate reaction zones, each having the hydroperoxide concentration maintained at an essentially uniform value throughout the zone. Naphthenates, octoates and stearates are among suitable catalysts.
U.S. Pat. No. 3,987,100, issued to Barnette et al. on Oct. 19, 1976, discloses cyclohexane oxidation in the presence of a binary catalyst system comprising specific amounts of chromium and cobalt, reacting any cyclohexyl hydroperoxide that may be formed in the presence of said binary catalyst system, and recovering a product consisting of cyclohexanone and cyclohexanol in a specified ratio.
U.S. Pat. No. 4,326,084, issued to Druliner et al. on Apr. 20, 1982, discloses an improved process for oxidizing cyclohexane to produce a reaction mixture containing cyclohexyl hydroperoxide and decomposing the cyclohexyl hydroperoxide to form a mixture containing cyclohexanone and cyclohexanol comprising using in the oxidation step and/or the decomposition step, as a catalyst, a transition metal complex of certain 1,3-bis(pyridylimino)isoindolines. Usable transition metals are cobalt, manganese and iron.
Semenchenko et al., Russ. J. Phys. Chem. 47 (5), 654, (1973) have found that the decomposition of CHHP in cyclohexane in the presence of cobalt stearate is initially rapid and then slows down, i.e., the activity of the catalyst falls rapidly as the hydroperoxide decomposes.
Certain cobalt complexes with anionic heterocyclic nitrogen-donor ligands apparently catalyze the decomposition of other organic hydroperoxides. For example, Hock and Kropf, J. Prakt. Chem. 9, 173, (1959) tested the phthalocyanine derivatives of seven different metals as catalysts for the autoxidation of cumene (isopropylbenzene). They found that cobalt phthalocyanine gave the highest overall conversion of cumene to oxidation products, the highest conversion of cumene to K/A mixture, and the lowest conversion to cumene hydroperoxide in the final product mixture. Since the ketone and alcohol (acetophenone and 2-phenyl-2-propanol) are known to be decomposition products of the hydroperoxide, it can be inferred that the cobalt compound was the best catalyst for the decomposition of the hydroperoxide. The amount of hydroperoxide in the final product mixture was small but significant, and corresponded to 5.8% of the cumene originally charged.
Kamiya, Kogyo Kagaku Zasshi 72 (8), 1693, (1969); Chem. Abstr. 72, 11793Y, (1970) reports that cobalt phthalocyanine was a better catalyst than cobalt dodecanoate in the oxidation of cumene, and for the autoxidation of ethylbenzene. In each case the activity was "due to the decomposition of hydroperoxides".
Ochiai, Tetrahedron 20, 1819, (1964) studied the mechanisms by which transition metal stearates and transition metal phthalocyanines, including those of cobalt, participate in the autoxidation of cyclohexene.
It is known that the use of cyclohexane-soluble Cr.sup.+3 complexes to catalyze the decomposition of CHHP offers the possibility of obtaining high K and A yields, high K/A ratio, and low DCHP formation. In order to achieve the yield improvement, the CHHP decomposition should be run at a temperature range of about 110.degree.-130.degree. C. However, CHHP decomposition with Cr.sup.+3 catalyst is also known to cause severe fouling and insufficient decomposition of CHHP and to be sensitive to adventitious impurities. A major cause of fouling is the presence of short chain carboxylic acids, such as acetic acid, which cause precipitation of chromium compounds. These acids can be removed by water washing the process stream; however, the water causes the formation of insoluble hydroxide complexes. A process which alleviates these problems is desirable.